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• below the haul road at switchbacks, and at both ends of the 2 percent benches. It is <br />recommended that an 18-inch minimum diameter CMP be used for these culverts. This <br />culvert will convey the maximum 1-foot design depth from the haul roads with 6-inches of <br />dry freeboard. Taking runoff through the switchback ai an approximate 10 percent grade, the <br />culvert will transport water at 14.1 cfs, above the 5.9 cfs design flow rate for the runoff <br />control ditches. The culvert should be covered with a minimum of 1-foot of cover. Regular <br />maintenance should be employed to keep haul road ditches and culverts clean. Proper end <br />sections should be installed to transition water from ditch to culvert and avoid upstream head <br />development. Placing the culvert invert just above the runoff ditch will provide a sediment <br />trap to further prevent clogging and head development. <br />Road cuts off the coal waste will primarily be done in bedrock. Because of the competent <br />nature of the outcrops and the existing road cuts above the site, the road cuts for the haul <br />roads were designed to be at 1:1 slopes. Fills at the switchbacks on the east side of the pile <br />will be constructed ai a 2: f slope. As required by Rule 4.03.1(3)(d), the fill should be <br />constructed on stripped foundation surface. Since the ground surface at this site is steeper <br />than 3:1, a 10-foot keyway is required. The fill should utilize material obtained from other <br />road cuts at the site. It should be clean of organic matter, and contain no coal-related <br />material. Compaction should be a minimum of 95 percent Standard Proctor compaction (D- <br />698, or AASHTO T-99) in maximum 12-inch lifts. Large particles that inhibit proper lift <br />development or compaction should be removed. Roads cut in unconsolidated material, as may <br />be the case for the initial eastern haul road, should be constructed at 2:1. A vegetative cover <br />should be placed to stabilize fills and cut slopes. Until fills and cut slopes can be stabilized <br />using vegetation, other means such as a silt fence may be used to control sediment. <br />The initial haul road located on the east side of the coal waste bank is outside of the disturbed <br />area. Runoff collected in the ditch will not be routed to the sediment pond. Silt fences and <br />revegetation will be used to capture sediment. Maintenance will be performed regularly to <br />remove collected sediment. Flows will be routed as necessary away from the road. <br />Haul roads will be surtaced with a minimum of six inches of crushed, durable rock material. <br />Surfaces will be graded to drain into adjacent drainage ditches, and will be maintained to avoid <br />ponding of water. <br />• <br />96266/7424.RPT Coal Mine Waste Bank Final Design for the Bowie No. 2 Mine <br />June 1998 W E S T E C 9 <br />aucguur-or <br />